1. Field of the Invention
The present invention relates to a pointing device utilized as an operating device for an electronic device such as a mobile phone, a PDA, or a game controller, and relates to a key sheet for the pointing device. More particularly, the present invention relates to a pointing device of a magnetic field detection type which detects a change in magnetic flux density resulting from movements made by a magnet, and relates to a key sheet for the pointing device.
2. Description of the Related Arts
Operating devices for electronic devices and their input modes have been diversified. There has been known a pointing device of a magnetic field detection type which detects a change in magnetic flux density resulting from “a lateral movement” of a magnet such as a tilt or a horizontal displacement by means of a magnetic field sensor and utilizes the detected change as an input signal.
As an example of such a pointing device of a magnetic field detection type as described above, there has been known a pointing device in which a magnetic field sensor is mounted on a reverse face of a printed circuit board so that the magnetic field sensor and the pointing device do not interfere with each other (see JP 2000-235822 A, FIG. 7). However, this causes a problem in that a space is required for the magnetic field sensor on the reverse face of the printed circuit board to be mounted, that reduces mounting efficiency. In view of this, there has been known another pointing device in which a magnetic field sensor is mounted on a front face of a printed circuit board (see JP 2002-150904, FIGS. 4 and 5), by which the problem can be eliminated.
However, in the case where the magnetic field sensor is mounted on the front side of the printed circuit board, the following problem is caused. This will be described hereinafter with reference to the drawing.
A pointing device 1 shown in FIG. 11 includes a key top 2 exposed through a penetration hole Ch of a casing C of an electronic device such as a mobile phone, a magnet 3, a base sheet 4, and magnetic field sensors 5 such as Hall elements mounted on a printed circuit board P. The base sheet 4 is formed of a thick support portion 4a, a thin flexible portion 4b, and a fixation portion 4c for the printed circuit board P. The key top 2 and the magnet 3 are firmly fixed to the support portion 4a. As shown in FIGS. 11(A) and 11(B), when the key top 2 is operated to be moved laterally leftwards in the drawings, the magnet 3 laterally moves together with the support portion 4a due to expansive and contractive deformation of the flexible portion 4b, and changes magnetic flux density, which is to be detected by the magnetic field sensors 5.
In the case of this example, however, even if the magnetic field sensors 5 are located on the front face of the printed circuit board P but below the support portion 4a of the base sheet 4, the support portion 4a may slide into contact with the magnetic field sensors 5 at the time of a lateral movement to a state shown in FIG. 11(B). Thus, a rupture may occur in the support portion 4a, or mounting conditions of the magnetic field sensors 5 with respect to the printed circuit board P may be adversely affected through sliding contact with the support portion 4a. Accordingly, the clearance between the support portion 4a and the front face of the printed circuit board P must be set large. But there is a limit to a reduction in thickness of the pointing device 1 and a demand for size reduction of electronic devices cannot be satisfied.